This testfile demonstrates an image that is missing "alt" text.
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html lang="en">
<head>
<title>alert 1.0/1.1.1</title>
</head>
<body>
<img src="noAlt.jpg"/>
</body>
</html>